Inhibiting corrosion of metal conductors



United States Patent 3,247,094 INHIBITIN G CORROSION 0F METAL CONDUCTORS Mahmoud Dajani, Park Forest, 111., assignor to Nalco Chemical Company, Chicago, 11]., a corporation of Delaware No Drawing. Filed Nov. 23, 1962, Ser. No. 239,814 11 Claims. (Cl. 20847) This invention is concerned with improvement of intermediate stages of refinery processes. More specifically, this invention relates to -a method of inhibiting corrosion of metal conductors used to convey and process normally liquid charge stocks which are later converted to usable liquid and gaseous hydrocarbon fuels.

In the past, various chemical additives have been used to treat finished petroleum products such as gasoline, kerosene, diesel fuels, finished solvents and the like in order to maintain stability of the products upon long standing and/or render them less corrosive to susceptible metals. However, until just recently little attention has been paid to treating intermediate charge stocks which are used in subsequent refining operations. These intermediate charge stocks are particularly corrosive and without treatment cause considerable damage both to metal conveyors stationed at various spots in the over-all petroleum refining process, and to the process units themselves. When these intermediate charge stocks are subjected to relatively high temperatures and/or pressure their corrosive tendencies increase beyond permissible limits. Consequently, it has been proposed that corrosion inhibitors also be injected into the refinery stream to render the intermediate charge stocks less corrosive. However, use of finished product corrosion inhibitors in process streams, has resulted in many failures due to extreme differences in character of treated petroleum hydrocarbon and charge stock, and complete dissimilarity of outside environment to which a finished petroleum product and charge stock are subjected. For example, charge stocks are almost invariably subjected to much higher temperatures relative to those temperatures at which the finished products are kept. Likewise, the atmospheric conditions surrounding the charged stock and finished petroleum products are completely dissimilar in many cases. Usually the charged stock is being subjected to a reducing atmosphere in presence of acids, sulphides, salts, water, etc., while the finished product must withstand an oxidizing attack and is in a relatively pure noncorrosive state before storage. Likewise the charge stocks are frequently put under high atmospheric pressure, while the petroleum products when stored are normally kept at atmospheric pressure. Thus, while known corrosion inhibitors such as dimerized fatty acids, exhibit satisfactory performance as finished product additives, they show little or no activity as refinery stream inhibitors of charge stocks.

With increasing demand for higher octane gasolines, improved aviation fuels and improved residual fuels it has therefore become the practice to treat the various refinery charge stocks with corrosion inhibitors specifically devised for that purpose whereby undesirable impurities are reduced to a minimum and improved fuel values are extracted from the subsequently processed products. Likewise, in order to increase equipment life, save on time-consuming shutdowns and decrease the tendency of metal conductors to impart corrosion deposits, scale, etc., to the flowing liquid or gaseous stocks, there has been found a need for a new class of corrosion inhibitors for this specialized finery operation. As mentioned above, the resort to conventional prior art corrosion inhibitors ordinarily used to treat finished products, often has little application to this specialized problem.

The charge stocks which are most commonly employed 3,2470% Patented Apr. 19, 1966 in the intermediate refinery processes, and which exhibit corrosive tendencies and impair corrodible metal surfaces may be chosen from among naphthas, gas oils, and crudes. The naphtha distillate stocks may be considered as a light oil, at least 10% of which boils below 347 F. and at least of which distills below 464 F. The gas oils which frequently are referred to as middle distillates usually are intermediates between the so-called kerosene fractions and the light lubricating cuts. These gas oils usually are used as charges to cracking units where the molecules are broken down into smaller components. The crude oils which most commonly cause the problem of corrosion are virgin products charged to the first refining stage operations containing all of the petroleum fractions normally removed in the refining processes. For the purposes of this invention, crude stocks are intended to cover the so-called residual or pot fractions which remain after the volatile components and solvent extractable components of the crudes which have been removed. Thus, it can be seen that the term charge stock is used generically to describe any petroleum hydrocarbon stock which may or may not have been already processed to some extent, usually the former, and which is destined for processing in at least one, and more commonly two or three refining steps in the over-all purification and separation of the many components going to make up pumped crude.

The various charge stocks mentioned above are most frequently subjected to one or more of the following general type processes to produce fuels: reforming, cracking, alkylation, isomerization, polymerization, desulfurization, hydrogenation, and dehydrogenation. These processes may be performed using a number of specific refining techniques which frequently employ catalytic reagents.

The types of mechanical equipment which are most commonly affected by the various corrosive charge stocks are furnaces, heat exchangers, reboilers and condensers. In these types of equipment, the charge stock is caused to flow through various types of heat processing devices which are part of or associated with the above equipment. For purposes of simplification such apparatus and devices associated therewith are referred to herein as conductors.

One of the most common spots for inhibitor addition is in the overhead line leading from the crude towers. This overhead line is used as a connection between the distillation tower and condensers. The distillate or stock which will be used to subsequently charge other refining processes, after being condensed upon the cooled surfaces of the condenser equipment is then caught in overhead accumulator drums. A portion of the distillate is recycled back into the crude pot with the majority being transferred to other refinery units.

Due to the extreme corrosivity of the crude distillate, it is almost essential to add inhibitor in this area of the refining process. However, many prior art inhibitors, and even those showing some activity as intermediate charge stock additives in other refinery areas show little or no effect in this specific application. This is due to a variety of reasons. For example, many failures result from resorting to inhibitors which are not effective over a wide range of pH of the water of the charge stocks and temperatures to which they are subjected. Even more important, since the virgin crude contains from less than 0.1% to about 10.0% water which is carried over into the accumulator drums it is necessary to separate by gravity this water phase from the hydrocarbon portions. However, in many cases this becomes extremely difiicult or even impossible since many corrosion inhibitors have a strong tendency to promote emulsification of the aqueous and hydrocarbon phases. Another drawback of inhibitors used in intermediate charge stocks is, while they may show satisfactory control in primarily aliphatic stock, they show little or no activity in stocks primarily composed of aromatics. Sometimesthe converse is true. It is necessary, for best effectiveness, that the inhibitor be both soluble in aliphatics and aromatics and mixtures of the two. Then the inhibitor is completely dispersed throughout the stock and more nearly complete protection is afforded.

A suitable corrosion inhibitor for intermediate charge stock when added at various points in the refining process such as overhead lines, must fulfill all the above conditions. In case of addition to an overhead line the inhibitor, for best results must be carried along with the charge stock into the various units and give protection to those units as well as metal storage containers or transfer lines. Likewise, some of the inhibitor preferably will be carried along with the recycle distillate going back into the crude towers and thereby help to decrease the corrosion rates in these towers as well.

It would be a valuable contribution to the art if the problems described above could be overcome by using chemical additives which not only meet the above described process requirements but are also economical and effective at relatively low dosages. This invention presents such asolution to this over-all problem.

It therefore becomes an object of the invention to provide chemical additives for use in intermediate refinery charge stocks, which additives show excellent corrosion protection over a wide range of pH and temperatures, exhibit necessary solubility in aliphatics, aromatics and mixtures ofsame and show little tendency to promote emulsification of aqueous and hydrocarbon phases.

A specific, object in the invention is to provide chemical corrosion inhibitors to intermediate charge stocks which remainefiective inhibitors in said stocks during subsequent transfer, storage, and processing, thereby protecting the equipment employed in such operations until the originally treated products are converted into different chemical species.

In accordance with the invention it has been found that intermediate refining process may be improved by incorporation into normally liquid, corrosive charge stocks at least a corrosion inhibiting amount of a mixed corrosion inhibitor comprising an amido-imidazoline and a diamide. The chargestock which normally flows through corrodible met-a1 conductors to other refining processes has its corrosive tendencies thereby inhibited by the above mixture. In particular, charge stocks comprised of gas oils, naphthas, and crude oils or mixtures of same may be suitably inhibited by this new class of corrosion preventatives.

In a specific embodiment the corrosion inhibitors are added just subsequent to distill-ations in crude towers and specifically to overhead lines leading to condensers and thence to overhead accumulator drums for distribution to a multitude of subsequent refining processes. The inhibitor, when added to such overhead lines has the tendency due to excellent solubility in aliphatics, aromatics, etc., to be carried onward with the charge stock, and also backinto the crude towers through various discharge lines. Normally, the charge stock is flowing through the various metal conductors under extremely corrosive conditions caused by high temperature, pressure, and environment, etc., such as in the immediate area of crude towers. Yet, the inhibitor of the invention is capable of control even under these adverse conditions. The inhibitor mixture of chemicals capable of preventing the corrosion is composed of a diamide having the following structural formula:

(1. the radical residue derived from naphthenic acid. The other portion of the mixture is an amido substituted imidazoline represented by the following structural formula:

H 1 -CHzCII2N ClIzCH2N-CR4 where R is an alkyl radical which preferably ranges from C to C y is an integer ranging from 0 to 2, and R is a radical derived from naphthenic acid.

The above corrosion inhibitor mixtures are simply prepared by a variety of known methods. In one embodi- 'ment a suitable source of a polyamine such as diethylene triamine, triethylene tetramine and tetraethylene pentamine or mixtures of the above or even raw materials containing minor amounts of other mono and polyamine impurities, is reacted with an unsaturated or saturated fatty acid in order to form the monoamide thereof. This reaction may be carried out at temperatures ranging from 40 C. to C. over times ranging from %8 hours. In a preferred embodiment a source of organic solvent such as benzene, toluene, xylene, etc., is used to help remove the water-by azeotropic distillation, thereby enhancingthe yield of monoamide. The fatty acid amidifying agents may be saturated or unsaturated. Illustrative of the saturated fatty acids are capric, lauric, myristic, palmitic, stearic and behenic. Unsaturated fatty acids used as amidifying agents include lauroleic, oleic, palmitoleic, myristoleic, linoleic, linolenic, and the like. The fatty acids may also be chosen from naturally-occurring sources in which a mixture of saturated and unsaturated fatty acids varying in their carbon content may be involved. For example, tallow, hydrogenated tallow, castor oil, palm oil, coconut oil, cottonseed oil, and the like may be employed as sources of amidifying agents. These natural sources vary widely as to their number and type of fatty acid constituents which go to make up the mixture. However, each of their fatty acid constituents falls within the scope of the invention and are particularly suited for use due to their low cost and availability. It has been determined that for best results fatty acids ranging from 8 to 22 carbon atoms in content show best results.

Necessarily formed in reaction of fatty acid and polyamine is a small amount of imiclazoline. Moreover, when the monoamides as prepared above are further reacted with a source of naphthenic acid, further ring closure is effected. In the majority of cases even when a predominantly diamide product is desired at least about 10% of amido-imidazoline is formed. However, such is not undesirable, and is in the fact preferred due to the enhanced solubility of the amido-imidazoline over that of the diamide in the various charge stocks, and particularly those containing a predominance of aliphatic components. Moreover, in either case whether the diamide component is predominantly produced or the amido-imidazoline, excellent corrosion inhibiting results have been noted.

The monoamide obtained above is then further reacted with an appropriate source of naphthenic acid in order to produce the diamide also containing varying amounts of amido-imidazoline. The diamides are appropriately prepared by reacting one mole of the formed monoamide with one mole of naphthenic acid. Generally the reaction is carried out at from 70 to 300 C. over a period of A1 to 8 hours duration or until one mole of water is removed. Normally it is carried out in from /2 to 3 hours time. Again, organic solvents may be used to promote removal of the water by azeotropic distillation. Also, a vacuum may be employed to strip off the organic solvent and any unreacted material or impurity therein. The monoamidification and diamidification reactions are well known and need little elaboration.

As mentioned above, after the monoamide of fatty acid and suitable polyamine has been formed, this in turn is reacted with a source of naphthenic acid. These are wellknown as monobasic carboxylic acids of the general formula R(CH COOH, where R is a cyclopentyl radical and n is an integer of 0 to 18. The R(CH' naphthenic radical is derived predominantly from cyclopentane or a homolog thereof, or sometimes from a bicyclic pentane derivative. The cyclopentane ring may have alkyl groups attached in various ways and in higher molecular weight naphthenic acids, double naphthenic groups may be present or even predominate. The carboxyl group is most often attached to a side chain, and less frequently attached directly to the ring. Naphthenic acids are present in most crude petroleums and are usually recovered from kerosene and gas-oil cuts in straight run petroleum distillation. Typically the preferred commercially available naphthenic acids have an acid number of 180220. However, grades having an acid number as low as 140 and as high as 360 are fully suitable for preparing the diamides and amidoimidazolines for use in the invention. A complete description of naphthenic acids is found in U.S. Patent 2,430,951 which is herein incorporated by reference.

Using the general techniques outlined above, mixtures have been formed containing up to 90% of diamide with the remainder composed primarily of amide-imidazoline in a type of equilibrium mixture.

If a mixture is desired which is composed predominantly of .arnido-imidazoline the following technique is employed. Again, the monoamide fatty acid and polyamine is synthesized as generally outlined above. However, in a second step a monoamide is then heated to relatively high temperatures, either by itself or in some high boiling azeotropic solvent such as toluene, whereby substantial ring closure is effected. In many cases up to 98% imidazoline has been obtained. This reaction is carried out at temperatures ranging from 100 C. to 280 C. over periods of time ranging from /2 hour to 14 hours. After the imidazoline has been formed the amino .alkyl substituent on the ring is then further reacted with naphthenic acid in order to form the amidoimidazoline. This reaction, like the monoamidification reaction above can be carried out either with or without solvent. Imidazolines or glyoxalidines employed as starting materials for further reaction with the naphthenic acids are made by well known procedures as described. For example, in Wilson, U.S. Patent 2,267,965 and Wilkes et al., U.S. Patent 2,268,273. The disclosures of these patents are also herein incorporated by reference. The corrosion mixture composed predominantly of the two above ingredients will contain anywhere from about 2 to about 90% by weight of diamide and from about to 98% by Weight of amido-imidazoline.

The following examples exhibit typical preparations of mixtures of diamide and amide-imidazoline. In Examples I, III, and IV, the diamide components of the mixture predominate, while in Examples II and V, the amidoimidazolines are in the greater proportion.

EXAMPLE I A 3-necked round bottom flask equipped with stirrer, condenser, Dean and Stark trap, thermometer and heating mantle connected to a Variable transformer is charged with 280 grams of oleic acid. To this is added 309 grams of diethylene tr-iamine and the entire mixture is solubilized in toluene. The reactants are heated at about 120 C. until one mole of water is driven off in the amidification reaction. The excess amine is then removed under vacuum distillation. To 73.2 grams of the above monoamide having an approximate molecular weight of 363 is added 70.7 grams of a source of naphthenic acid whose molecular weight is approximately 350. Suflicient toluene is added to completely solubilize the mixture and it is then heated at approximately 120 C. The refluxing toluene acts to pull off the water eliminated in the diamide production. The reaction is continued until approximately the theoretical amount of water is removed by azeotropic distillation. The toluene is then stripped off under reduced pressure and the product isolated. The product comprises approximately 86% of diamide and 14% amide-imidazoline. The test for imidazoline content is made using the standard salicylaldehyde test involving formation of a Schiifs base with primary amines and phenylthioisocyanate (reaction with primary and secondary amines) technique.

EXAMPLE II In this example the monoamide of Example I is first synthesized into an imidazoline by application of heat. The monoamide product is reacted at 275 C. for 3 hours in order to form the imidazoline derivative by ring closure technique. To this imidazoline is then added naphthenic acid on a mole to mole basis, which mixture is then heated for a total of 4 hours at 150 C. The final product analyzed 92.3% amido-imidazoline with the remainder being predominantly composed of diamide.

EXAMPLE III In this example the procedure of Example I was followed with the exception that hydrogenated tallow fatty acid was substituted for oleic acid in making the monoamide on a mole for mole basis.

EXAMPLE IV The experimental techniques of Example I were followed except caprylic fatty acid was employed.

EXAMPLE V The procedure of Example IV was employed in this experiment except hydrogenated tallow fatty acid was used in place of oleic acid.

The above mixture of compositions are used at dosages ranging from as little as .1 p.p.m. to as high as 300 to 500 p.p.m. The optimum treatment level which will work is dependent upon the type of charge stock, type of intermediate refining operation to which the stock is subjected, the temperature at which the particular process is performed, pressure under which the stock is placed, etc. As a general rule, the dosage range of the crudes will be between 0.5 p.p.m. and 300 p.p.m. In the case of naphthas, the dosage range will be between 0.1 p.p.m. and 200 p.p.m., with a preferred treating range between 0.1 .and p.p.m. When gas oils are treated, the dosage may vary from 0.5 p.p.m. to 300 p.p.m., with optimum dosage levels being between 1 and 100 p.p.m.

One of the most interesting features of the invention is that a portion of the additive remains preferentially with the liquid phase of the charge stock during the various refining stages. Other portions of the additive act to form a film upon the surfaces of the metal conductors. Thus, not only is protection provided for equipment through which the liquid charge stock is flowing at a given moment, but also equipment and metal conductors through which the charge stock has already been transferred remain protected for subsequent liquid flow. Thus, the additives may be added to the charge stock at any point in the process and will be carried along with the stock until such a point in the refining operation where the product is converted to a different chemical component or species.

As mentioned above, a particularly preferred point of application is in the overhead lines which are used to carry off the distillate from the crude towers. Another area in which the inhibitor mixture may be added is prior to the heat exchange section of a thermal distillation unit used to remove lighter fraction. This protection will be afforded to both exchanger surface and other surfaces of the distillation or fractionation unit.

Many advantages have been realized through use of the mixture of corrosion inhibitors of the invention in intermediate refining processes which prior art applicants have not been able to meet either in part or in toto. For example, one of the most important advantages is ability to afford excellent corrosion protection over a wide range of pH and temperatures. This will be exhibited in more complete detail below. Due to the extreme differences in the nature of various petroleum crudes, and in particular the nature and amount of their corrosive impurities, an effective corrosion inhibitor must maintain its activity over a wide range of pH and must show control in both acid and basic environment. In particular, the compositions of the invention show excellent corrosion protection at pHs ranging from 1 to 11 and more preferably from 4 to 8. Likewise, since the multitudinous refinery processes are effected at temperatures varying over a wide range, a multipurpose corrosion inhibitor must show equally good results at lower relative temperatures as well as the normally more corrosive higher temperatures.

Another excellent property of the corrosion inhibitor mixture of the invention is its negligible tendency to promote emulsification. Ase generally outlined above, most virgin oils have small amounts of water contained therein. The aqueous phase, of course, is carried over in the various distillations effected in the intermediate refinery system, and the water must be separated from the hydrocarbon phase in order to give the desired fuel products. However, many prior art inhibitors have a strong tendency to promote emulsification such as in overhead accumulator drums whereby the heavier aqueous phase cannot be withdrawn from the lighter petroleum fractions. In such a case numerous shutdowns occur, or long standing storage periods are necessary to obtain the desired sharp separation of aqueous and hydrocarbon phases. Also, in most instances an uneconomical loss of product occurs. At the very least, de-emulsifying agents may have to be added thereto. Such resort to extraneous process steps of chemical additives is not necessary in practice of the instant invention.

The product of Example II was specifically tested in a typical West Coast refinery as to its tendency to promote emulsification. The chemical was added to an overhead line leading from a crude still. This line Was connected to condensers which in turn led to an overhead accumulator drum. Ten p.p.m. of the chemical was added to the overhead line, and every few hours the drum was inspected. A sharp clean separation of aqueous and hydrocarbon phase was noted at all times, allowing the heavier water to be easily and economically withdrawn from the drum without resort to extraneous chemical addition or further processing.

In addition to the above enumerated advantages, the corrosion inhibitors of the invention also show excellent solubility in a wide variety of aliphatic, aromatic, etc. solvents. The specific diamide-amido-imidazoline corrosion inhibitor mixture of Example II was tested for solubility characteristics in a number of specific solvents. These included isooctane, kerosene, white gasoline, naphtha, and mineral seal oil. In each of these solvents the composition showed complete miscibility in all proportions.

Evaluation of the invention In order to test the effectiveness of the compositions of the invention in inhibiting corrosion, a specific test was devised which closely approximated conditions in a typical intermediate refining process. Also, test oil solutions were made which were similar to a composite charge stock. Tests were run using 25% kerosene solutions of the compositions of Examples I, III, and IV at various additive dosages. Also, a number of different metals were tested as to protection afforded and the temperatures and pHs were varied to get a more complete picture of the versatility of the compositions. Refinery stream overhead conditions as simulated in the laboratory set-up consisted of a corrosive atmosphere comprising hydrocarbon, low

solids, water and nitrogen-air-hydrogen sulfide gases. Corrosion rates were determined by weight differences that result from exposing a mild steel or other metal coupon to this atmosphere for 18 hours. The test procedure is generally as follows. A 1000 ml. round bottom three-neck Pyrex flask fitted with a stirrer shaft, stirrer blade, condenser, gas dispersion tube, cork stopper, coupon holder and heating mantle were set up as equipment. The corrosion coupon was a 0.9525 cm. in.) x 3.81 cm, 1 in.) x 0.317 cm. /s in.) S.A.E. 1020 mild steel coupon. A 0.317 cm. diameter hole was drilled or punched through one of the coupons not less than 0.317 cm. from the edge. Prior to this the coupon had been sandblasted and weighed. The test solution, simulating a refinery charge stock, consisted of a depolarized naphtha and treated water. The naphtha had been treated prior to use with activated alumina by agitation with the alumina for one hour after which it was filtered through fullers earth. 425 ccs. of the above depolarized naphtha and 22.5 cos. of a refinery stream water, which was composed of 1000 p.p.m. hydrochloric acid' and 500 p.p.m. of acetic acid Whose pH was adjusted to the desired level with ammonium hydroxide, was charged into the apparatus. Inhibitor was also added at this point. The pH ranges and temperatures used in the test were pH 1.8-2.5 and 6.9-7.6 at room temperatures and 1.8-2.5, 4.2-4.5 and 6.9-7.6 at 200 F. A gas phase was continuously introduced above the liquid phase during the test. This gas phase consisted of 93% prepurified nitrogen, 5% air, and 3% hydrogen sulfide, and was fed at a rate of 40 cc./minute per test by means of calibrated capillary tubing. After the waternaphtha had been placed in the flask, the gas tube holder was inserted into the flask neck and the flow of gas turned on. Agitation was then effected and heating applied (if required). The test was allowed to run for one hour before the coupon was inserted. This was done to attain equilibrium and obtain more meaningful value. The coupon was positioned so that the gas dispersion tube was on the downstream side of the coupon. Therefore, the gas made a complete circuit of the flask before it contacted the coupon,

At the end of the test, the coupon was removed from the flask, cleaned with cleansing powder to remove loose corrosion products, dipped with mild agitation in an inhibited acid bath for- 30 seconds, dipped in a saturated soda ash bath for 20 seconds, washed in tap water to remove remaining salts, dipped with agitation in an acetone bath and spun dry. The coupon was then dried in a 100 F. oven for 30 minutes and reweighed. All corrosion rates can be determined on a basis of coupon size and test duration, however, for corrosion inhibitor evaluation purposes, the weight loss from treated tests are compared vvith weight losses from untreated test at equivalent pHs.

The above test was modified somewhat in order to test the effect of the corrosion inhibitors of the invention on Admiralty metal. In this case the oil phase was 400 ml. depolarized filtered heptane and the water phase consisted of ml. of aqueous test solution prepared by adding 1000 p.p.m. HCl and p.p.m. H 3 to deionized water. After the acid and sulfide were added enough ammonium hydroxide was slowly added to adjust the pH to the required value. After this adjustment 100 p.p.m. of sodium cyanide were added. The tests on the Admiralty metal were run at room temperatures at pH 8.5-9.5 and 9.2-11.3 and at :10 F. at pH 8.5-9.5.

Tables I-VIII below show the corrosion test results run at the indicated temperatures. The pH and dosage were varied as indicated and results are given in percent protection. In some cases comparison was made with prior art known corrosion inhibitors. In all cases the active corrosion ingredients were compounded into 25% kerosene solutions. The corrosion rates of the untreated blank coupons are given in mils per year.

TABLE I.STEEL-ROOM TEMPERATURE-pH 1.8-2.5

[Blank (154 MPY)] P.p.m. formula Inhibitor Example IV" 38 65 74 91 93 Example I 28 75 88 93 Polymeric Amine. 40 85 TABLE H:STEELROOM TEMPERATURE-pH 6.97.6

[Blank (48 MPY)] P.p.m. of formula Inhibitor Example IV- t 43 67 47 Example I- 65 82 27 Amine Salt 53 60 84 TABLE IIL-STEEL-200" F.pH 1.8-2.4

[Blank (300 MPY)] P.p.m. formula Inhibitor Example IV 45 69 94 Example I 41 82 94 Amine Salt 6 20 51 TABLE lV.STEEL-200 F.pH 4.2-4.5

[Blank (200 MPY)] P.p.m. formula Inhibitor Example IV 35 83 Example I 51.0 91

TABLE V.STEEL200 F.pH 6.9-7.6 [Blank (231 MPY)] P.p.m. formula Inhibitor I Example IV 35 83 93 94 Example I 42 92 94 Amine Salt 58 75 TABLE VI.--ADMIRALIY85RO OM TEMPE RATURE-pH [Blank (46 MPY)] l P.p.m. formula Inhibitor Example I 55 55 70 7s 55 TABLE V1I.-ADMIRALTY92R3)M TEMPERATURE-pH: 1

[Blank (446 MPY)] P.p.m. formula Inhibitor E xample I 5 52 84 95 TAB LE VlII.-ADMI RALTY-160 Fl0 F.pH:8.5-9.5

P.p.rn. formula Inhibitor Example I 24 59 71 78 77 The above results show the excellent corrosion inhibitory action of representative samples of the compositions of the invention. Extreme versatility under adverse conditions of varying pH, temperature, etc., are to be noted. The corrosion mixtures when primarily composed of amido imidazolines are as effective or in many cases more effective due to increased solubility as compared to the above which are primarily diamides.

Another advantage in using the corrosion inhibitors of the invention in treatment of various petroleum charge stocks is reduction of a phenomenon now recognized and descriptively called fouling. This phenomenon manifests itself in the form of deposits which frequently form on the metal surfaces of the processing equipment and tend to materially decrease the efficiency of the intermediate refining operations. The direct results of fouling appear in the forms of heat transfer loss, decreased pressure drops, loss throughput and, in some instances, a specific type of corrosion product is associated -with the deposists. These deposits are most likely to occur at elevated temperatures which range between 200 F. and 1100 F, and may be either organic, inorganic, or mixed organic and inorganic, with the latter type deposit being the most common type found in intermediate refining processes. The organic deposits are primarily polymerization products and are usually black, gummy masses which may be converted to coke-like masses at elevated temperatures. The inorganic portions of the deposit frequently contained components of silica, iron oxide, sulfur trioxide, iron sulfide, calcium oxide, magnesium oxide, inorganic chloride salts, sodium oxide, alumina, sodium sulfate, copper oxides and copper salts. The diamide-amido imidazoline mixtures tend not only to materially decrease corrosion, but also tend to prevent formation of the above deposits and/or remove them if once formed.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

The invention is claimed as follows:

1. An improved intermediate refining process for petroleum hydrocarbons used to produce liquid and gaseous hydrocarbon fuels which comprises the step of adding at least a corrosion inhibiting amount of a mixed corrosion inhibitor to a heated, intermediate normally liquid, corrosive charge stock flowing through corrodible metal conductors, whereby corrosion of said conductors by said stock is substantially reduced, said inhibitor mixture consisting essentially of 290% by weight of a diamide having the following structural formula:

Rr--N-{CH2CI-I2NH)x where R is an alkyl radical containing 1-22 carbon atoms, R is a radical derived from naphthenic acid having an acid number within the range Olf to 360, x is an integer ranging from 1 to 3; and tl0-98% by weight of an amido-imidazoline represented by the structural formula:

where R is an alkyl radical contain-ing 721 carbon atoms, R; is a radical derived from naphthenic acid having an acid number within the range of 140 to 360 and y is an integer ranging from to 2.

2. The process of claim 1 wherein said charge stock is a petroleum hydrocarbon liquid selected from-thegroup consisting of crude oils, gas oils and naphthas.

3. The process of claim 1 whereby sufficient inhibitor additive is maintained in saidcharge stock so as to inhibit corrosion of corrodible metal equipment used in processing said stock subsequent to inhibitor addition. 3

4. The process of claim 1 wherein R is an alkyl. radical containing from 8.t0 22 carbon atoms, at is 1 and y is,Q.

, 5. An improved intermediate refining process for petroleum hydrocanbons used to produce liquid and gaseous hydrocarbons which comprises the steps of adding at least .1 p.p.m. of a corrosion inhibitor mixture to a heated, intermediate, normally liquid corrosive charged stock flowing through corrodible metal conductors :to subsequent conversion process units, lwhereby corrosion of .said conductors and said units by said stock is substantially reduced, said charge stock being selected from the group consisting of gas oils and naphthas which have been distilled from crude oil towers, and said inhibitors mixture consisting essentially of 290% by weight of a diamide having the following structural formula: I

Rio1 rcHzcH2Nn CHZOHzNAl-Ri where R is an alkyl radical containing 1-22 carbon atoms, R is a' radical derived from naphthen-ic acid, having an acid number within the range of 140 to 360,

x is an integer ranging from 1 to 3, and l0-98% by weight of an amido-imidazoline represented by thestructural formula: I g

where R is an alkyl radical containing -7-21 carbon atoms, y is an integer ranging from 0 to 2 and R is a radical derived from naphthenic acid having an acid number within the range of 140 to 360.

6. The method of claim 5 whereby suflicient inhibitor additive is maintained in said charge stock so as to inhibit corrosion of corrodible metal equipment used 111 processing said stock subsequent to inhibitor addition.

and 1098% by weight of an amido-imidazoline represented by the structural formula:

I 10. corrosion inhibitor useful in inhibitingthe corrosion of normally liquid corrosive charge stocks used in intermediate 'refining processes, which consists essentially of a corrosion inhibitor mixture consisting essentially of 290% by weight ofa diamide having the following structural formula:

1098% by weight of an amino-imidazoline represented by the formula:

wherein 'R 'is 'an alkyl radical containing 1-22 carbon atoms and R is analkyl radical containing 7-21 carbon 1 atoms, at is: an integer ranging from 1 to 3, y is an integer ranging from 0 to 2, and R and R are radicals derived from naphthenic acid having an acid number within the range of to 360, said composition being further characterized as being soluble in both aliphatic and aromatic solvents from the class consisting of isooctane, kerosene,

' white gasoline, naphtha and mineral seal oil, andas having substantially little tendency to promote emulsification ofliquid aqueous and hydrocarbon phases.

11. The composition of claim 10 where R, is an alkyl radical-containing from 8 to 22 carbon atoms, x is 1 and JULIUS GREENWALD, Primary Examiner.

' ALBERT T. MEYERS, Examinen UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,247,094 April 19, 1966 Mahmoud Daj ani It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 68, for "finery" read refinery column 9, in TABLE II fourth column, for [li' read M l g Signed and sealed this 22nd day of August 1967,

(SEAL) Attest:

EDWARD Jo BRENNER ERNEST W. SWIDER Commissioner of Patents Attesting Officer 

1. AN IMPROVED INTERMEDIATE REFINING PROCESS FOR PETROLEUM HYDROCARBONS USED TO PRODUCE LIQUID AND GASEOUS HYDROCARBON FUELS WHICH COMPRISES THE STEP OF ADDING AT LEAST A CORROSION INHIBITING AMOUNT OF A MIXED CORROSION INHIBITOR TO A HEATED, INTERMEDIATE NORMALLY LIQUID, CORROSIVE CHARGE STOCK FLOWING THROUGH CORRODIBLE METAL CONDUCTORS, WHEREBY CORROSION OF SAID CONDUCTORS BY SAID STOCK IS SUBSTANTIALLY REDUCED, SAID INHIBITOR MIXTURE CONSISTING ESSENTIALLY OF 2-90% BY WEIGHT OF A DIAMIDE HAVING ATHE FOLLOWING STRUCTURAL FORMULA: 